Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device. More particular, the present invention relates to an OLED display device capable of sensing and correcting a progressive bright point defect, and a method of driving the same.
Discussion of the Related Art
A liquid crystal display (LCD) using a liquid crystal, an organic light emitting diode (OLED) display device using an OLED, an electrophoretic display (EPD) using electrophoretic particles, etc. have been generally used as a flat panel display device that displays an image using digital data.
Among the above-mentioned devices, the OLED display device is a self-emissive device that allows an organic light emitting layer to emit light through recombination of an electron and a positive hole. The OLED display device has a high luminance and a low driving voltage and may be configured as an ultra-thin film. Thus, the OLED display device is expected to be used as a next generation display device.
Each of a plurality of pixels or sub-pixels included in the OLED display device has an OLED element that includes an organic light emitting layer between an anode and a cathode and a pixel circuit that independently drives the OLED element.
The pixel circuit includes a switching thin film transistor (TFT) that supplies a data voltage such that a storage capacitor is charged with a voltage corresponding to the data voltage, a driving TFT that controls a current based on the voltage with which the storage capacitor is charged and supplies the current to the OLED element, etc. The OLED element generates light in proportion to the current. The current supplied to the OLED element is affected by driving characteristics such as threshold voltage (Vth), mobility, etc. of the driving TFT.
However, the threshold voltage, the mobility, etc. of the driving TFT differ between sub-pixels for various reasons. For example, an initial threshold voltage, a mobility, etc. of the driving TFT differ between sub-pixels due to process variation, etc., and a difference occurs between sub-pixels due to deterioration of the driving TFT, etc. that occurs as a driving time passes. As a result, currents of the respective sub-pixels are non-uniform for the same data, and thus a problem of non-uniform luminance occurs. To solve this problem, the OLED display device uses an external compensation method of compensating for data by sensing the driving characteristics of the driving TFT.
For example, the external compensation method senses a voltage (or a current) indicating a driving characteristic of each driving TFT, computes compensation values for compensating for variations of a threshold voltage and a mobility of the driving TFT based on the sensed value to store the compensation values in a memory or update values, and then compensates for data to be supplied to each sub-pixel using the stored compensation values.
The OLED display device has a problem of a minute short-circuit defect due to particles, etc. that enter during a manufacturing process. The minute short-circuit defect is not detected in an inspection process, etc. prior to product shipping. However, when a driving time passes after product shipping, a resistance component due to the particles gradually decreases. In this way, short-circuit is generated, which leads to a progressive bright point defect.
Therefore, while a short-circuit defect detected in the inspection process may be corrected to be darkened by being repaired, the progressive bright point defect, which is not detected in the inspection process and found with the lapse of a driving time due to the minute short-circuit defect, may neither be detected nor corrected.